Upanishads, Yogasutras of Patanjali and teachings of Gautam Buddha, all talk about "the right speech". As per Gautam Buddha, the right speech has three components:

1. It should be based on truthfulness.
2. It should be necessary.
3. It should be kind.

All three have to be in the same sequence with truthfulness taking the top ranking. For example, when a patient asks a doctor, "Am I going to die in the next few weeks or will I survive longer?" The truth may be that he is serious enough and may not survive but it is not necessary to speak the truth and also it is not kind. Therefore, that truth should not be spoken.

Lord Krishna in Mahabharata explained when not to speak the truth and when to speak a lie. The truth which is going to harm the society may not be spoken and a lie which can save the life of a person without harming others may be spoken.

1. A truth which is necessary and kind may be spoken.
2. A truth which is not necessary but kind may not be spoken.
3. A truth which is necessary but not kind may not be spoken.
4. A truth which is neither necessary and nor kind may not be spoken.

(Disclaimer: The views expressed in this write up are my own).